Dear Metallo,

Hope you're well and stay so. Glad that the problem was not with the valves!

The oil filler cap has a rubber gasket. The gasket slowly hardens as the rubber is "cooked" by engine heat. A hard gasket likely does not seal properly. So, before getting a new oil filler cap, replace the gasket.

This is Volvo Part #940096. At a U.S.-based Volvo dealer it costs about $8. It should be readily available elsewhere.

As your engine is a Turbo, it likely does not have a "flame-trap". On non-turbo engines, if that part - a plastic insert with a number of small holes - is plugged with "gunk", the blockage can cause crankcase over-pressure. Oil is forced past seals, etc.

I presume your car does have an oil breather box - mounted on the right side of the engine, as you face it, below the intake manifold - where oil vapor from the head (where hot oil circulates) is condensed and returned to the oil pan. If the oil breather box is clogged, that, too can lead to elevated crankcase pressure.

Hope this helps.

Yours faithfully,

Spook